Power supply



Nov. 18, 1952 G. D. HULST 2,618,773

POWER SUPPLY Filed Aug. 5, 1949 Fig. 3

IN V EN TOR.

64 GEORGE 0. HULST Fig. 5

w gww Patented Nov. 18, 1952 UNITED STATES PATENT OFFICE POWER SUPPLY Application August 3, 1949, Serial N 0. 108,323

6 Claims.

This invention relates to power supplies for use with cathode ray apparatus and the like, and more particularly to power supplies for use in a television receiver.

In a television receiver, the second anode of the cathode ray tube which provides the accelerating force for the electron beam, is connected to a power source producing a positive direct potential of between 10 and 25 kilovolts, the higher voltages being in general more satisfactory for larger diameter and brighter picture tubes.

Voltage supplies producing this order of voltage usually have employed high voltage insulators cast from a special electrical ceramic material such as porcelain or glass. Such materials are not, however, adaptable for use in a television receiver because of their brittle nature. For this reason, plastic materials have been used as insulators for high voltage supplies in television receivers. Of these plastic materials, the most useful ones for the purpose have been thermosetting plastics, such as phenolics. Phenolics have excellent mechanical properties, do not exhibit cold flow, can be coated to prevent surface leakage, are inexpensive, and are easily molded or machined. Nevertheless, in spite of these desirable properties, the phenolics have not been used as high voltage insulators generally in high quality receivers, because of their tendency to carbonize in high voltage gradients and become conductive, causing eventual breakdown of the insulator and making the receiver inoperative.

It is an object of my invention to provide high voltage apparatus for use in a television receiver which completely prevents the carbonization of phenolic insulators.

It is a second object to provide apparatus which is inexpensive to produce, and which lends itself readily to manufacturing processes.

It is a further object to provide a structure which allows a voltage gradient of 10 kilovolts per inch in a phenolic insulator, permitting a compact and mechanically rigid arrangement of high voltage parts.

In the drawings:

Figure 1 shows schematically a circuit incorporating the invention;

Figure 2 is a side view of an embodiment with a portion broken away to show the construction;

and

Figures 3, 4 and 5 show electrical fields and physical characteristics to illustrate the operation of the invention.

Referring to Figure 1, a transformer I2 has its primary winding connected between a source I3 of positive potential and the anode of 2. rectifier tube I4. A driving tube I5, having a signal grid I6, is connected to a tap on the primary winding. The secondary winding of the transformer I2 is connected to a filament type thermionic cathode of the rectifier tube I4 through the resistor I'I. One side of the filament is connected to a filter capacitor l8, to a filter resistor l9, and to a conductive member 2I constructed preferably cup-shaped in accordance with my invention. The other end of the resistor I9 is connected to a second filter capacitor 22 and to a high voltage output lead 23 which, in the preferred application, is connected to the second anode of a television picture tube.

In Figure 2, where parts shown in Figure l are designated by the same numerals, a lead 25 connecting the primary of the transformer I2 to the anode of the rectifier tube I4 is made with a diameter of approximately inch to avoid corona. The base 26 of the rectifier tube I4 is inserted into an octal Socket 2'! of the wafer type in common use in television receivers. The wafer socket is mounted on metallic posts 28 by means of screws 29. The posts 28 are supported in turn by the metallic cup-shaped member 2|, and fastened thereto by the screws 32. This member 2I is preferably formed from aluminum sheet by a simple punching process well known to the fabrication art and as such can be mass produced at low cost. In the punching process the edge of the cup-shaped member 2I is preferably formed into a rounded lip 33 having a, diameter of approximately A; inch to avoid corona.

The cup shaped member H is mounted on the chassis 34 by means of phenolic stand-ofi insulators 35 and screws 36, providing a compact, inexpensive, and highly desirable construction when assembled in accordance with the invention as will be more fully explained below.

The octal socket 21 contains eight base terminals 4I-48 corresponding respectively to terminals I-B of standardized octal socket terminology. The elements and wires may be connected to the desired terminals before assembly of the socket 21 with the conductive member 2I. The resistor I9 is connected between base terminals 42 and 46. The resistor I1 is connected between the terminals 44 and 41. The terminal 42 is also connected to the metallic post 28, forming thereby a conductive path between terminal 42 and the cup-shaped member 2|. This last connection may be omitted if the leakage resistance of the octal socket 21 is low compared to the resistance of the insulators 35, a condition which usually has been found to exist. Circuit elements connected to the tube socket, and operating at high potentials, are within the space enveloped by the cup-shaped element 2|, thus avoiding the necessity of element corona shields.

The terminals t2 and 44 are connected to the secondary of the transformer l2 by means of the conductive wires 52 and 53, respectively. The terminals 42 and 46 are connected to filter capacitors I8 and 22 by means of conductive wires 54 and 55, respectively, the latter connection being made by connectors 56 which have a rounded external contour to prevent corona. For the same purpose the conductors 52-55 have a diameter of approximately inch. The filter capacitors I 6 and 22 are connected rigidly by one terminal to the chassis.

The fundamental operation of the voltage supply is well known. An alternating voltage is applied to the grid 15 of the driving tube causing acurrent from the source l3 to flow therein intermittently. When the current through the tube is cut off by the action of the grid, a high positive voltage peak occurs in the primary of the transformer l2 causing the filter capacitor to receive-a positive charge through the rectifier tube M. This charge is filtered of alternating current components by the action of the elements l9 and 22- and applied to a direct current load such as the second anode of a cathode ray picture tube. The resistor I! may be chosen to provide desired power in the filament of the rectifier tube hi.

The operation of the conductive member 2i may be understood by referring to Figures 3, land 5. In Figure 3, the conductive member 2| is charged up to a high positive direct potential during the operation of the set. Regions of suc- A cessively lower potential surfaces are indicated by the lines 62. It will be noticed that the surfaces 34 and 21 tangent to the insulating members 35' are essentially parallel, the insulating members extending at right angles thereto, so that the equipotential surfaces pass through the supporting insulators at almost right angles to the axes thereof, thereby assuring a uniform potential gradient within. the insulator. Under these conditions phenolic may be used as an insulating material without danger of. progressing carbonization and ultimate destruction.

In Figure 4 there is shown an octal socket 21 mounted directly on stand-01f insulators 35 without the: use of the conductive member 2|. The lines 62 in' this figure, drawn approximately Where the equipotential. surfaces occur, tend to bunch around the protruding. terminals of the socket as indicated by the numeral '63. The bunchingi of lines is indicative of a high potential gradient" in this region. If a phenolic insulator is used, this .high gradient is destructivacausing carbonization in the direction of the electric field. Once the carboniz'ation commences, the process of destruction becomes cumulative, sincethe carbonized portions are'conductive, forming high potential fields at their ends and causing tentacles of carbonized matter to grow atboth ends, in the direction of the field. The growth of carbonized matter is shown in Figure 5, where the antlerlike carbon tentacles '64 are shown before the process of carbonization has resulted in complete destruction. The condition shown is typical ofthose found in television receivers" where the conductivemember'zi had been omitted; The

length of time required for complete destruction varied from several weeks to over a year, the reasons for the differences in time not being known, since the several sets had been made as similar to one another as was practical using ordinary production care. In all of these cases, no visible or audible indication of the destructive process was present until the last stages. By the addition of the conductive member 2|, a potential gradient of 10 kilovolts per inch can be maintained for an indefinite period of time under a wide variety of temperature and humidity conditions.

In the preferred form shown, a phenolic insulator of homogeneous material is used. It is believed that stable operation under the high potential gradient here shown require this. If an insulator is formed of an aggregate of dissimilar materials, having differing dielectric constants or resistivities, there may occur local points of increased potential gradient, causing carbonizeti'on. Therefore it is believed advisable to use a homogeneous material.

Although a specific embodiment has been shown and described, other embodiments will be readily understood from the teachings above. The scope of my invention, therefore, will be best understood by referring to the following claims.

What is claimedis:

1. In a high voltage supply, a planar conductive surface substantially at ground potential, a homogeneous insulating member attached to and extending at right angles from said surface, a tube socket having terminals at high potentials,

- and a conductive member charged substantially to said high potentials partially enclosing said socket, said conductive member being supported by and having a surface adjacent said insulating member, said adjacent surface being essentially planar and parallel to said conductive surface.

21 In a high voltage supply, a planar conductive'surface substantially at ground potential, a homogeneous insulating member attached toand extending at right angles from said surface,- an insulating support for high potential circuit elements, and a conductive member charged to high potential partially enclosing said support, said conductive member being supported by and having a surface adjacent said insulating member, said adj aoent surface being essentially planar and parallel to saidconductive surface.

3'. In a. television receiver, a chassis, a direct current voltage supply comprising a source of alternating voltage, a rectifier tube connected in series with said source, a socket for said tube having high potential terminals, an electrically conductive member charged to high potential partially enclosing said'soc'ket, and a homogeneous insulating. member supporting said conductive member and extending between said conductive member and said chassis, said chassis and conductive member being substantially planar and mutually parallel inthe vicinity of said insulating member.

4. In a high voltage supply, a planar conductive surface substantially at ground potential, a homogeneous insulating member attached to and extendingfat right angles from said surface, and a conductive member supported by said insulating member and having a planar surface adjacent said insulating member essentially parallel to said conductive surface, said conductive member be ing charged to a potential in kilovol-t*units approximately ten times the length of said phenolic member in inches.

5. In a high voltage supply, an electrically con ductive planar surface substantially at ground potential, a homogeneous insulating member attached to and extending at right angles from said surface, a conductive member supported by and having a surface adjacent said insulating member, said adjacent surface being essentially planar and parallel to said conductive surface, an aperture in said conductive member, an electrically conductive high-voltage junction structure partially enclosed Within and connected to said conductive member, and conductive Wires attached to said junction structure and extending through said aperture.

6. In a television receiver, a chassis, a direct current supply comprising a source of alternating voltage, a rectifier tube connected in series with said source, a socket for said tube, a circuit element at high potential connected between terminals of said socket, a conductive member partially enclosing said socket and said element and charged substantially to said high potential, and

a homogeneous insulating member supporting said conductive member and extending between said conductive member and said chassis, said chassis and conductive member being substantially planar and mutually parallel in the vicinity of said insulating member.

GEORGE D. HULST.

OTHER REFEREITCES Television H. V., R-F Supplies, Mautner et al., RCA Review, March 1947, Vol. 8, N0. 1, D13- 43-81. 

